1. Field of the Invention
The present invention relates to a rock crushing device for crushing a rock by the utilization of an expandable member which is, after being inserted into a borehole formed in the rock, expanded by the pressure of a liquid material injected thereinto, and a method thereof.
2. Description of the Prior Art
In recent years, a crushing device of the type referred to above using an expandable member has been developed that crushes the rock in the following manner. Namely, after the expandable member made of rubber or synthetic resin is inserted into a borehole formed in the rock to be crushed, a liquid material is pumped into the expandable member by a high-pressure pump. Due to the expansive pressure of the expandable member acting on the wall of the borehole, a crack or cracks are produced in the rock.
Moreover, if a plurality of expandable members are inserted into boreholes formed in the rock one for each borehole, and the liquid material is pumped into these expandable members by a single pump at one time, a high crushing efficiency can be achieved by the above crushing device.
However, in the prior art crushing device as mentioned above, if the liquid material is continuously supplied even when cracks are generated in the rock by the expandable members pressed against the walls of the boreholes, the cracks become still larger in size and some of the expandable members may enter into the cracks, resulting in undesirable breakage or damage to the expandable members.
Accordingly, for avoiding damage to the expandable members, although it is enough to stop the supply of the liquid material when the cracks are generated, it has been considerably difficult to make sure whether the cracks are really generated in the rock, since the rock mass is not uniform in its nature, due to its having joints or hard and soft portions.
Further, when a plurality of boreholes are to be crushed instantaneously, it is a disadvantage that the cracks cannot be formed simultaneously in the boreholes. In many cases, even when cracks are generated in some of the boreholes, a crack is not formed in the others. Moreover, an additional supply of the liquid material after the generation of the cracks in the boreholes causes adverse effects to the expandable members in the cracked boreholes. In other words, the cracks become larger and the expandable members easily come into the cracks, thereby being damaged and disabled. Once some of the expandable members are damaged, the remaining ones cannot be applied with more pressure due to a leakage of the liquid material from the damaged one, resulting in the impossibility of crushing the rock. Thus, the prior art crushing device is disadvantageous in that it has low operating efficiency and is uneconomical.